Ovaries reveal their inner testes

From Nature:

News.2009.1135 Inside every ovary lurks a testicle just waiting to develop. So says a study in mice that further overturns traditional views of sexual development — and reveals that females must constantly suppress their masculine side.

Mathias Treier, a geneticist at the European Molecular Biology Laboratory in Heidelberg, Germany, and his colleagues deleted a gene called FOXL2 in sexually mature mouse ovaries. When they examined the ovaries three weeks later, they had switched sex and started pumping out the hormone testosterone. “The major finding is that females must actively suppress the male pathway inside the ovary,” Treier says. “Here is a gene that is not located on the sex chromosome that makes you stay female.”

More here.